1. Field of the Invention
The present invention relates to a method for controlling authorization for access to an object, in which a signal communication via electromagnetic waves is established between the object and a wireless portable unit when a tripping device on the object is actuated. The signal communication comprises (includes) at least a first signal that is sent from the object to the portable unit and at least a second signal that is sent from the portable unit to the object in response to the first signal(s). The second signal(s) comprises sufficient information to verify that the portable unit has an approved identity (verification information can be checked) and a distance is measured between the object and the portable unit so that authorization is confirmed if both the checked verification information is approved and the measured distance is less than a predetermined value. The predetermined value corresponds to a maximal permitted distance between the portable unit and the object.
The invention will be described below for authorization control for a vehicle, such as a car or truck. This is a preferred, but in no way limiting, application of the invention. In such a case, the tripping device normally consists of a door handle on the vehicle.
More specifically, the field of the invention is aimed at a so-called passive access control, which means that the person who is authorized to access the object does not need to actively use any key or remote control in order to unlock the object's door. Instead, the authorization is checked automatically via the abovementioned signal communication using electromagnetic waves between the vehicle and the wireless unit carried by the person, when the vehicle's door handle is actuated. The door is unlocked automatically in the event of approved authorization.
2. Background Art
U.S. Pat. No. 5,723,911 relates to a device for controlling access to a motor vehicle. This control is designed to be carried out without the user needing to actuate any key. A distance detection device on a transceiver carried by the user is designed to detect the distance between the transceiver and the vehicle with the aim of reducing the risk of unauthorized access to the vehicle. The authorization control is carried out by a transmitter in the vehicle sending a call signal to a receiver in the transceiver when the vehicle's door handle is actuated. The transmitted signal has a short range. The transceiver's receiver receives the signal and sends a coded response signal back to the vehicle only if the vehicle is in the immediate vicinity of the transceiver. In other words, no response signal is sent back to the vehicle if this is not located in the vicinity of the transceiver. A receiving unit in the vehicle receives the response signal, checks it and sends an unlocking signal to the lock if the response signal is correct. The distance detection is carried out, for example, via transmission of a distance detection signal from the transceiver and reflection of this by the vehicle.
The distance detection is carried out as mentioned above with the aim of reducing the risk of unauthorized access to the vehicle. Such unauthorized access to the vehicle has previously been possible by the use of a pair of receiver-transmitters in the following way: a first person with a first transmitter-receiver is in the vicinity of the vehicle while a second person with a second transmitter-receiver stands in the vicinity of the authorized user of the vehicle. The first person actuates the door handle of the vehicle, which initiates the signal communication. The signal (with a short range) from the vehicle's transmitter is received by the first person's receiver and forwarded with a long range to the transmitter-receiver of the second person and thereafter to the rightful user of the vehicle. In the same way, the coded signal is thereafter sent back from the portable unit to the vehicle via the two pairs of transmitters-receivers and authorization is confirmed.
Using the distance detection device according to U.S. Pat. No. 5,723,911, the time it takes for the electromagnetic waves or ultrasound waves to go from the portable unit to the object and back again is measured. If the rightful user is located at a great distance from the vehicle, the transmission of the ultrasound waves takes a long time. This is detected and a signal is not sent back to the vehicle from the portable unit.
A problem with this distance detection device is that it is not possible to know for certain that it is the correct (authorized) portable unit that is in the vicinity of the right vehicle. In addition, known methods for distance detection, such as ultrasound echoes and metal detection, are relatively easy to deceive and are thus not secure.